The outer body has a waist part defined as a front-back direction range with the side seal portions (front-back direction area ranging from the waist opening to the upper ends of the leg openings) and an intermediate portion defined as a front-back direction range forming the leg openings. In general, the intermediate portion has cover parts positioned on the lateral sides of the inner body, and elastic members such as rubber threads or sheets are provided in the waist part and the cover parts (for example, refer to Patent Documents 1 and 2).
However, the conventional underpants-type disposable diapers have a problem of an insufficient fit to the lower part of a gluteal region. Specifically, the waist part of the outer body is entirely cylindrical, and when elastic members are provided in a state extended in a width direction to the waist part, the elastic members exert a contraction force to tighten the entire waist part and fit to the wearer's body without looseness. Meanwhile, the cover parts have width-direction outer ends (edges of the leg openings) made free, and are likely to be insufficient in their fit even when elastic members are provided in the extended state to the cover parts. In particular, the cover parts of the outer body in the back body are portions to cover the lower bulging part of a gluteal region, and the width-direction outer ends of the cover parts, that is, the edges of the leg openings are likely to lift and flap under influence of the bulge of the gluteal region.
To deal with this problem, providing elastic members along the edges of the leg openings has been proposed as described in Patent Document 1. However, the addition of the members would unfavorably increase manufacture costs and bring about reduction in flexibility and air permeability.